Ink for white reflective film, powder coating material for white reflective film, production method of white reflective film, white reflective film, light source mount, and lighting device shade

ABSTRACT

There is provided an ink for white reflective film formation including: a liquid binder resin component containing a crosslinkable silicone liquid resin and crosslinkable silicone resin particles; and titanium oxide particles, the ink containing 10 to 500 parts by mass of the titanium oxide particles relative to a solid content of a total of 100 parts by mass in the liquid binder resin component.

This is a Division of application Ser. No. 14/765,118 filed Jul. 31,2015, which in turn is a national stage of PCT/JP2014/001036, filed Feb.26, 2014, which claims the benefit of JP 2013-037974, filed Feb. 27,2013. The disclosure of the prior applications is hereby incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a white reflective film for use as areflector or the like to reflect light emitted from a light source tothe side where the light is to be applied, such white reflective filmformed around a light emitting portion of light sources such as an LEDdevice and an LED element or formed on the surface of a light sourcemount; and also, for use as a reflector or the like to reflect sunlightfor concentration into a solar photovoltaic device.

BACKGROUND ART

Conventionally, there has been known a white reflective film formed as areflector to reflect light emitted from a light source to the side wherethe light is to be applied. For example, Patent Literature 1 mentionedbelow discloses a white reflective film formed from a titaniumoxide-containing silicone composition comprising: silicone; andanataze-type or rutile-type titanium oxide particles dispersed in thesilicone. Such white reflective film is disclosed as not showing signsof yellow discoloration or deterioration with time and as highlyreflecting high-intensity light of a wide range of wavelengths over along period of time.

For a titanium oxide-containing silicone resin composition for forming awhite reflective film as described above, a liquid ink has beenconventionally used.

The ink is applied to the surface of a base member and then thermallycured. As a method for applying the ink, methods such as screenprinting, roll coating, spray coating, and knife coating can be given.Preferred among these, is coating formation by screen printing whereinthe ink is applied via a mesh screen, in terms of excellentcontrollability of the coating thickness.

Incidentally, a powder coating material including silicone and titaniumoxide has been conventionally known. Most powder coating materialsincluding silicone are used to impart stain repellency to the surface ofproducts. For example, Patent Literature 2 mentioned below discloses afluorine-containing resin powder coating material compositioncontaining: fluorine-containing resin powder coating material particles(a); and methyl silicone resin particles (b) including photocatalytictitanium dioxide, wherein: the particles (a) and the particles (b) arecontained substantially independently of each other; and the content ofthe particles (b) is 1 to 25 parts by mass relative to 100 parts by massof the particles (a). Patent Literature 2 also discloses that thecoating formed from such composition has a self-cleaning ability byphotocatalysis; and that since the coating maintains excellentweatherproof performance of the fluorine-containing resin, the surfaceof products can remain maintenance-free over a long period of time. Thepurpose of this fluorine-containing resin powder coating materialcomposition is to form a coating that imparts stain repellency to thesurface of products.

Patent Literature 3 discloses a powder coating material compositionhaving excellent heat resistance and adhesion at a high temperature of300° C. or more. Specifically, Patent Literature 3 discloses a powdercoating material composition wherein: a binder component is a siliconeresin used singly, or a mixture of a silicone resin and at least oneresin selected from an epoxy resin, a phenolic resin, an acrylic resin,a polyester resin, and a fluorocarbon resin; at least one of mica andwhisker is contained as a reinforcing pigment; and the content of thesilicone resin in the binder component is 60 wt % or more. The purposeof this powder coating material composition is to form a heat-resistantcoating.

PRIOR ART Patent Literature

-   [Patent Literature 1] WO2010-150880 pamphlet-   [Patent Literature 2] Japanese Laid-Open Patent Publication No.    2003-176440-   [Patent Literature 3] Japanese Laid-Open Patent Publication No.    2004-27146

SUMMARY OF INVENTION Technical Problem

When a white reflective film is formed, a high degree of pencil hardnessis difficult to obtain. When the hardness of the surface of a whitereflective film is of a low degree, there are problems such as dustattaching thereto and reflectance thereof gradually lowering due to finescratches created thereon. Moreover, when a white reflective film isformed by applying ink, it may be difficult to form a coating withuniform thickness on the surface of products having a complexthree-dimensional shape.

Solution to Problem

One aspect of the present invention is an ink for white reflective filmcontaining a crosslinkable silicone liquid resin, crosslinkable siliconeresin particles, and titanium oxide particles, the ink containing 10 to500 parts by mass of the titanium oxide particles relative to a solidcontent of a total of 100 parts by mass in the crosslinkable siliconeliquid resin and the crosslinkable silicone resin particles.

Another aspect of the present invention is a production method of whitereflective film including: a step of forming a coating by screenprinting or roll coating the foregoing ink for white reflective filmonto a base member; and a step of thermally curing the coating.

Still another aspect of the present invention is a powder coatingmaterial for white reflective film containing: a crosslinkable siliconesolid resin; and 10 to 500 parts by mass of titanium oxide particlesrelative to 100 parts by mass of the crosslinkable silicone solid resin.

Further aspects of the present invention are: a white reflective filmhaving an initial reflectance for light at a wavelength of 550 nm thatis 80% or more and a pencil scratch hardness that is 8 B or higher, andcontaining a cured silicone resin and 10 to 500 parts by mass oftitanium oxide particles relative to 100 parts by mass of the curedsilicone resin; a light source mount or a lighting device shade with theforegoing white reflective film formed thereon.

Advantageous Effects of Invention

According to the present invention, there is obtained a white reflectivefilm having excellent hardness and reflectance, the reflectance notbeing likely to lower with time.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1F are schematic sectional illustrations of a step-by-stepdepiction of a method for forming a white reflective film by screenprinting.

FIG. 2 is an explanatory illustration schematically depicting theleveling of a coating of an ink for white reflective film formed byscreen printing.

FIG. 3 is a schematic sectional illustration depicting the mounting of alight source onto a circuit board whereon a white reflective film isformed.

FIG. 4 is a schematic sectional illustration depicting a lighting deviceshade whereon a white reflective film is formed.

FIG. 5 is an image of when the surface of a white reflective film formedby screen printing in Example 11 was magnified about 147 times with amicroscope for observation.

FIG. 6 is an image of when the surface of a white reflective film formedby screen printing in Example 17 was magnified about 147 times with amicroscope for observation.

FIG. 7 shows the measurement results for the reflectance of a 50μm-thick white reflective film obtained in Example 1.

DESCRIPTION OF EMBODIMENTS

[Embodiment 1]

The present inventors studied on the cause of the lowering inreflectance of a white reflective film which used silicone. As a result,they found that when the white reflective film had a low degree ofhardness, dust attached to the surface or fine scratches were created onthe surface, thereby causing reflectance to gradually lower with time.Thus, a white reflective film having a pencil scratch hardness of 8 B orhigher was obtained by using silicone resin instead of silicone such assoft silicone rubber. Specifically, the white reflective film having apencil scratch hardness of 8 B or higher was obtained by using a resincomposition containing a crosslinkable silicone resin and titanium oxideparticles, the content of the titanium oxide particles being 10 to 500parts by mass relative to 100 parts by mass of the cross linkablesilicone resin. According to such white reflective film, occurrences ofproblems as described above can be suppressed. In the following, adetailed description will be given of an ink for white reflective filmfor forming a white reflective film of the present embodiment(hereafter, also simply referred to as ink), a base member for applyingthe ink, a forming method, properties of the white reflective film, andothers.

(Crosslinkable Silicone Resin)

The crosslinkable silicone resin is a resin component having, as aprincipal skeleton, a siloxane skeleton that forms a polymer with athree-dimensional network structure that is highly-branched and denseobtained by a thermosetting treatment. The term crosslinkable in thepresent embodiment means the non-crosslinked or non-cured state of theresin having a reactive functional group that cures by forming achemical bond by a curing treatment, and may be otherwise termed ascurable. Further specifically, the crosslinkable silicone resin is anearly condensation polymer that contains: trifunctional siloxane units(T units) originating from monomer units represented by RSiX₃ (where: Ris an alkyl group, e.g., a methyl group, or a phenyl group; and X is ahydroxyl group or a hydrolyzable functional group, e.g., an alkoxygroup); and as necessary, bifunctional siloxane units (D units)originating from monomer units represented by R₂SiX₂ and/ortetrafunctional siloxane units (Q units) originating from monomer unitsrepresented by RSiX₄, that is contained by being combined with the Tunits, and that stops a dehydration-condensation reaction betweensilanol groups at an early stage of the reaction. Such crosslinkablesilicone resin forms a cured product having a three-dimensional networkstructure including a siloxane skeleton as the principal skeleton, byundergoing a curing treatment whereby unreacted silanol groups in theresin are dehydrated and condensed. The silicone resin may be a siliconeresin formed by addition polymerization, or may be a network-likepolysiloxane such as silsesquioxane that is synthesized by conductinghydrolysis on alkyltrialkoxysilane or the like having three hydrolyzablegroups, and then conducting condensation polymerization on theresultant.

The crosslinkable silicone resin may be an unmodified silicone resin(straight silicone resin) having only R groups with alkyl groups, phenylgroups, or a combination of alkyl groups and phenyl groups as sidechains; or may be a polyester-modified, acrylic-modified,epoxy-modified, alkyd-modified, or silicone rubber-modified siliconeresin that is modified by causing an organic resin having an alcoholichydroxyl group or the like to react with a hydroxyl group at themolecular end, with an alkoxy group that is a part of a silanol group,or with the like.

The crosslinkable silicone resin is usually in liquid or solid form atroom temperature; and can be obtained as commercially-available productsfrom, for example, Momentive Performance Materials Japan LLC., WackerAsahikasei Silicone Co., Ltd., and Shin-Etsu Chemical Co., Ltd.

In such crosslinkable silicone resins, a curing catalyst is included asnecessary. The curing catalyst is not particularly limited if capable offacilitating a curing reaction that allows condensation of a condensablegroup such as a silanol group or an alkoxy group in the silicone resin.Specific examples include curing catalysts that are aluminum-based(e.g., DX-9740 available from Shin-Etsu Chemical Co., Ltd.),titanium-based (e.g., D-20 and D-25 available from Shin-Etsu ChemicalCo., Ltd.), phosphorous-based (e.g., X-40-2309A available from Shin-EtsuChemical Co., Ltd.), and zinc-based.

(Crosslinkable Silicone Liquid Resin)

The crosslinkable silicone liquid resin can be obtained as acommercially-available product from, for example, Shin-Etsu ChemicalCo., Ltd. Specifically, examples of a varnish of an unmodified siliconeresin include: KR-400 and KR-242A being varnishes of a dimethyl-basedstraight silicone resin having a methyl group; and KR-271, KR-282,KR-300, and KR-311 being varnishes of a methyl phenyl-based straightsilicone resin having a methyl group and a phenyl group. Examples of avarnish of a modified silicone resin include: KR-5230 and KR-5235 beingvarnishes of a polyester-modified silicone resin; KR-1001N and ES-1023being varnishes of an epoxy-modified silicone resin; KR-9706 being avarnish of an acryl-modified silicone resin; and KR-5206 being a varnishof an alkyd-modified silicone resin.

The crosslinkable silicone liquid resin may be a crosslinkable siliconeliquid resin varnish of a solventless type; or a crosslinkable siliconeliquid resin that is dissolved, or, diluted with a solvent for viscosityadjustment. The solvent is not particularly limited. Specific examplesinclude toluene, xylene, n-butylalcohol, isopropylalcohol,diacetonealcohol, propyleneglycol monomethyletheracetate,3-methyl-3-methoxybutyacetate, and methylethylketone. These may be usedsingly or in a combination of two or more.

The solid content concentration of the crosslinkable silicone liquidresin, when including an organic solvent, is preferably 10 to 80 mass %and further preferably 20 to 70 mass %. When the solid contentconcentration is too low, the titanium oxide particles tend toprecipitate or volatilization of the organic solvent after applicationtends to take too much time. When the solid content concentration is toohigh, application tends to become difficult due to increased viscosity.The solution viscosity of the crosslinkable silicone liquid resin ispreferably about less than 10 Pa·sec and further preferably about 0.0001to 1 Pa·sec.

Preferably used as the crosslinkable silicone liquid resin, is acrosslinkable silicone resin capable of having a pencil scratch hardnessof preferably 9 B to 7 H, further preferably 3 B to 7 H, andparticularly preferably F to 6 H, when in the form of a 50 μm-thickcured film. Such crosslinkable silicone resin is preferably a dimethylstraight silicone resin wherein the R group is a methyl group, a methylphenyl-based straight silicone resin wherein the R group is acombination of a methyl group and a phenyl group, or the like, whichcontains siloxane units of D units and siloxane units of T units.Particularly preferable is a dimethyl-based straight silicone resin or amethyl phenyl-based straight silicone resin, wherein: the degree offunctionality (number of moles of T units/number of moles of D units)derived from the ratio between the D units and the T units is preferably2.6 to 2.9 and further preferably 2.6 to 2.8; and the proportion of thephenyl group in the R group is preferably 20 to 60 mol % and furtherpreferably 30 to 50%. Also preferable is a modification of the abovedimethyl-based straight silicone resin or methyl phenyl-based straightsilicone resin such as a polyester-modified silicone resin, anacryl-modified silicone resin, or an epoxy-modified silicone resin.

(Crosslinkable Silicone Resin Particles)

The crosslinkable silicone resin particles are, for example, apulverized substance of a crosslinkable silicone solid resin. Specificexamples of the crosslinkable silicone solid resin include unmodifiedsilicone resins such as: YR3370 (Momentive Performance Materials JapanLLC) being a dimethyl-based straight silicone resin having a methylgroup; SILRES MK and SILRES 610 (available from Wacker AsahikaseiSilicone Co., Ltd.); and SILRES 604 (available from Wacker AsahikaseiSilicone Co., Ltd.) being a methyl phenyl-based straight silicone resinhaving a methyl group and a phenyl group. When dissolved, each of thesecrosslinkable silicone solid resins can be used as a crosslinkablesilicone liquid resin.

The crosslinkable silicone resin particles are obtained, for example, bypulverizing the crosslinkable silicone solid resin with a pulverizersuch as a jet mill or an atomizer; and then, as necessary, classifyingthe resultant with a cyclone classifier or the like. The crosslinkablesilicone resin particles and the titanium oxide particles may formcomposite particles by being melted and kneaded at a temperature equalto or more than the melting point of the crosslinkable silicone resinparticles to become a kneaded substance, which is then pulverized. Thecrosslinkable silicone resin particles have a melting point ofpreferably 45 to 200° C., further preferably 60 to 150° C., andparticularly preferably 70 to 130° C.

The average particle size of the crosslinkable silicone resin particlesor the composite particles is not particularly limited and is preferablyabout 0.5 to 100 μm, further preferably about 10 to 80 μm, andparticularly preferably about 15 to 50 μm. When the average particlesize of the crosslinkable silicone resin particles or the compositeparticles is too large, when the particles are included in the ink forimproving leveling performance as described below, in screen printingfor example, the crosslinkable silicone resin particles tend not to passthrough the screen mesh and tend to remain in the residual ink fromsqueegeeing; and the amount of the particles in the coating tend todecrease. When the average particle size of the crosslinkable siliconeresin particles or the composite particles is too small, when theparticles are included in the ink for improving leveling performance asdescribed below, melt flowability at the time of thermosetting tend tolower; and the effect of improving leveling performance tends not to beobtained sufficiently. The average particle size corresponds to themedian value (D₅₀) obtained by measurement using a laser diffractionparticle size analyzer.

(Titanium Oxide)

For a specific example of the titanium oxide particles, rutile-typetitanium oxide particles are preferable. Rutile-type titanium oxideparticles are low in photocatalytic activity, and therefore suppresslowering in reflectance due to deterioration of the white reflectivefilm caused by photocatalytic activity. Rutile-type titanium oxidefurther increases reflectance for the long wavelength region of 500 nmor more; whereas anatase-type titanium oxide further increasesreflectance for the short wavelength region of 420 nm or less. Thetitanium oxide particles are not particularly limited in shape and ispreferably spherical in terms of the particles having further increasedreflectance.

The titanium oxide particles may be surface treated to suppressphotocatalytic activity. For an inorganic surface treatment agent, zincoxide, silica, alumina, zirconia, or the like can be arbitrarilyselected.

The titanium oxide particles are preferably treated with a titaniumcoupling agent, an aluminate coupling agent, or a silane coupling agent.Treatment using these coupling agents may be conducted on the titaniumoxide that has been treated with the inorganic surface treatment agent.Treating the titanium oxide particles with a silane coupling agent ispreferable in terms of improving dispersibility and also increasing thefilm strength of the white reflective film. Specific examples of asilane coupling agent include coupling agents having a reactivefunctional group such as a vinyl group, a phenyl group, an alkoxy group,a glycidyl group, a (meta)acryloyl group, or the like. Further specificexamples include CH₂═CHSi(OCH₃)₃ (vinyltrimethoxysilane), C₆H₅Si(OCH₃)₃,C₂H₃O—CH₂O(CH₂)₃Si(OCH₃)₃, C₂H₃O—CH₂O(CH₂)₃SiCH₃(OCH₃)₂,CH₂═CH—CO—O(CH₂)₃SiCH₃(OCH₃)₂, CH₂═CCH₃—CO—O(CH₂)₃SiCH₃(OCH₃)₂,2-(2,3-epoxypropyloxypropyl)-2, 4,6,8-tetramethyl-cyclotetrasiloxane,2-(2,3-epoxypropyloxypropyl)-2, and 4,6,8-tetramethyl-6-(trimethoxysilylethyl) cyclotetrasiloxane.

The average particle size of the titanium oxide particles is notparticularly limited and is preferably 0.4 μm or less and furtherpreferably 0.1 to 0.3 μm in terms of reflection efficiency andapplication suitability. The maximum particle size is preferably 1 μm orless. A larger maximum particle size tends to reduce smoothness afterapplication.

(Preparation of Ink)

The ink is prepared by arranging the crosslinkable silicone liquidresin, the titanium oxide particles, and, as necessary, othercomponent(s), in a predetermined ratio; and then mixing the resultantwith a roller mill such as a three-roller mill or a five-roller mill, aball mill, or the like. As described later, for the purpose of improvingleveling performance, the crosslinkable silicone solid resin particlesmay be arranged as the crosslinkable silicone resin.

The solution viscosity of the ink is not particularly limited, and isarbitrarily adjusted in accordance with factors such as the kind ofcoater, the application amount, and, in the case of screen printing, themesh size. Specifically, the solution viscosity is, for example,preferably 10 to 800 Pa·sec and further preferably 20 to 600 Pa·sec, andalso further preferably 100 to 300 Pa·sec. In the case of screenprinting, when the viscosity is too high, the ink tends to remain on thescreen mesh and transferability tends to lower. When the viscosity istoo low, only the crosslinkable silicone liquid resin tends to flowduring leveling and the titanium oxide particles tend to be unevenlydistributed. Viscosity corresponds to a value obtained by a measurementby a “method using a single cylinder rotational viscometer” incompliance with JIS K7117, conducted at room temperature (25° C.)

The proportion of the titanium oxide particles in the ink is 10 to 500parts by mass, preferably 20 to 400 parts by mass, and furtherpreferably 30 to 300 parts by mass, relative to 100 parts by mass of thecrosslinkable silicone resin (solid content). When the proportion of thetitanium oxide particles is less than 10 parts by mass, it becomesdifficult to obtain an initial reflectance of 80% or more for light at,for example, a wavelength in a wide range such as 420 to 900 nm. Whenthe proportion of the titanium oxide particles exceeds 500 parts bymass, coating formability degrades such that, for example, the coatingbecomes fragile and cracks occur therein.

The hardness of the cured film of the crosslinkable silicone resin canalso be adjusted by, for example, mixing two or more kinds ofcrosslinkable silicone resins having different degrees of hardness. Thehardness can also be adjusted by adjusting the crosslink density byarranging to include, as necessary, a crosslinkable silicone oil, amonofunctional reactive diluent, or the like. The hardness can be alsobe reduced by mixing a resin component having a low degree of hardnesssuch as silicone rubber. The proportions of the crosslinkable siliconeoil and the silicone rubber are each preferably 0.5 to 10 parts by massand further preferably 1 to 5 parts by mass relative to a solid contentof 100 parts by mass in the crosslinkable silicone resin.

To the ink, substances other than the titanium oxide particles such asan inorganic white filler and an organic or inorganic fluorescentsubstance may be added to the extent of not inhibiting the effects ofthe present invention. Additives such as an adhesion modifier and aleveling modifier may also be added. Specific examples of an inorganicwhite filler include alumina, barium sulfate, magnesia, aluminumnitride, boron nitride, barium titanate, kaolin, silica, talc, powderedmica, powdered glass, powdered aluminum, powdered nickel, calciumcarbonate, zinc oxide, aluminum hydroxide, and magnesium hydroxide.These may be used singly or in a combination of two or more. In terms ofimproving heat conductivity of the white reflective film, alumina andaluminum nitride are preferred. In terms of improving reflectance withdecreased amount of the titanium oxide, which is expensive, andincreased amount of a light reflective pigment, which is less expensive,while also suppressing lowering in reflectance, barium sulfate, calciumcarbonate, and the like are preferred. In terms of improving fireretardancy, aluminum hydroxide and magnesium hydroxide are preferred.Specific examples of a fluorescent substance include a CASN-basedfluorescent substance, a silicate-based fluorescent substance, a garnetfluorescent substance such as a sialon-based fluorescent substance, asilicate salt fluorescent substance, a nitride/oxynitride fluorescentsubstance, a sulfide fluorescent substance, and a YAG-based fluorescentsubstance. Particularly, when forming the white reflective film around alight source that emits light having a wavelength of 300 to 420 nm suchas ultraviolet light, near-ultraviolet light, or blue light, awavelength conversion function can also be imparted to the whitereflective film by adding an organic or inorganic fluorescent substanceor the like that is brought into an excited state by lighting at 300 to420 nm. Since the ink of the present embodiment is a composition forforming a white reflective film that exhibits high light reflectance,black-colored or dark-colored elements are substantially not included.

In the ink, for the purpose of improving leveling performance, thecrosslinkable silicone solid resin particles, composite particles of thecrosslinkable silicone solid resin and the titanium oxide, or the likemay be included as the crosslinkable silicone resin. By including thecrosslinkable silicone solid resin particles or the composite particlesin the ink, during thermosetting of the coating, the crosslinkablesilicone solid resin melts and flows, and in association therewith, thetitanium oxide particles move as well, thereby smoothing the coatingsurface.

(Base Member)

The white reflective film is preferably formed on, for example: thesurface of a light source mount such as a circuit board for mounting alight source; the surface of a lighting device shade; the surface of alighting device housing; and a reflective material that reflectssunlight to a light-receiving element (e.g., solar photovoltaic element)so that the sunlight is concentrated thereat, or the surface andsurrounding area of a mount for such light-receiving element. The whitereflective film is also used as a reflector of a light conducting paththat improves light conductivity, by being formed at the interfacebetween light conducting plates or between light conducting sheets. Assuch, the white reflective film is used as a reflector formed in variousproducts that require high light reflectivity.

Specific examples of a light source include a light emitting diode(LED), an organic EL element, a common incandescent lamp, and afluorescent lamp.

Specific examples of a light source mount include sheets, films, andmolded bodies in planar or three-dimensional form that are configured tomount a light source. These may have a circuit for mounting the lightsource. When these form a stacked structure, the inner layer(s) may havea circuit thereon, or a vapor-deposited metal or a metal foil laminatedthereon. When the white reflective film is formed to cover the circuit,the film becomes a resist film that protects the circuit.

Specific examples of a circuit board include: a rigid or flexiblecircuit board provided with a circuit for mounting a light source; asubmount for mounting the light emitting element; and athree-dimensional circuit board.

The kind of the base member is not particularly limited. Examplesinclude: plates and foils made of metals such as copper and aluminum;planar substrates, three-dimensional substrates, and shaped bodies ofceramics such as aluminum nitride and alumina; glass-reinforced epoxysubstrates; and rigid substrates, flexible sheets, flexible films,three-dimensional substrates, and molded bodies made of materials suchas polyethylene naphthalate (PEN), polyacrylate, polycarbonate (PC),polysulfone (PSF), polyethersulfone (PES), polyimide (PI),polyetherimide (PEI), polyether ether ketone (PEEK), amorphouspolyacrylate (PAR), liquid crystal polymer (LCP), polyethyleneterephthalate (PET), and bismaleimide triazine (BT), and also, stackedbodies and stacked circuit boards wherein a vapor-deposited metal or ametal foil is laminated on the base members. The base member may also bea substrate in plate or sheet form obtained, for example, byimpregnating a sheet such as a glass cloth or a non-woven glass fabricwith the ink of the present embodiment. The base member may also be afilm for forming a coverlay film.

The surface of the base member may be surface treated as necessary, inorder to increase adhesion strength of the white reflective film.Specific examples of surface treatment include chemical surfacetreatments and/or physical surface treatments such as corona dischargetreatment, plasma treatment, ultraviolet light treatment, flametreatment, ITRO treatment, surface roughening treatment, primingtreatment whereby a silane coupling agent is applied, blastingtreatment, chemical etching, rubbing treatment, and/or cleaningtreatment using an organic-based solvent; and/or combinations ofchemical surface treatment and physical surface treatment.

(Formation of White Reflective Film)

The ink is applied to the surface of the base member, resulting information of a coating with a predetermined thickness; and then thecoating is then cured, thereby to form a white reflective film. Themethod for applying the ink is not particularly limited and is selectedin accordance with factors such as the coating thickness and the basemember form. Specific examples include screen printing, roll coating,spray coating, comma coating, knife coating, dip coating, dispensing,spin coating, and brushing. Among these, screen printing and rollcoating are preferred in terms of easy formation of a coating with auniform thickness.

When the coating is formed by applying the ink, unevenness andunintended imprints may remain thereon depending on the applicationmethod used. Specifically, for example, screen mesh imprints from screenprinting or roll patterns from roll coating may remain on the coatingsurface. In order to lessen such screen mesh imprints and roll patterns,the crosslinkable silicone resin particles that are solid, compositeparticles of the crosslinkable silicone solid resin and the titaniumoxide, or the like are preferably included in the ink. By including thecrosslinkable silicone resin particles that are solid or compositeparticles in the ink, during thermosetting of the coating, thecrosslinkable silicone resin that are solid melts and flows, and inassociation therewith, the titanium oxide particles move as well,thereby smoothing the coating surface.

The coating is cured by cross-linking of the crosslinkable siliconeresin. To cure the coating, a suitable method is selected fromphotocuring, room temperature curing, and the like, in accordance withthe kind of the crosslinkable silicone resin. Among these, thermosettingis particularly preferred. Even when photocuring or room temperaturecuring is used, thermosetting is preferably used in a combinationtherewith.

In the case of thermosetting, the coating is preferably cured at atemperature of preferably 120 to 300° C., further preferably 150 to 250°C., and particularly preferably 180 to 200° C. In the case ofphotocuring, the coating is preferably cured by using an ultravioletlight emitting device which emits light having a wavelength of 330 to450 nm, i.e., ultraviolet light, and light having a wavelength of 500 to600 nm, i.e., visible light. In the case of room temperature curing, forexample, there is a method wherein the coating is cured by being left atroom temperature for several days. Curing conditions are not limited tothose above and are arbitrarily selected in accordance with theproperties of the crosslinkable silicone resin and the base member.However, curing is preferably conducted in a combination withthermosetting.

Silicone usually contains a very small amount of unreactedlow-molecular-weight siloxane originating from the starting material ofthe silicone. For example, when the white reflective film is formed on acircuit board that is eventually heat treated in a solder reflow processor the like, the low-molecular-weight siloxane becomes volatilized bythe heat treatment. Such low-molecular-weight siloxane attaches to anelectronic circuit and an electronic element, and sometimes becomes thecause of poor adhesion of solder during the reflow process conductedthereafter as well as poor adhesion when connecting a gold wire to theelement. In order to lessen such low-molecular-weight siloxane in thewhite reflective film, by using a hot-air circulating oven, the film ispreferably thermoset at about 180 to 250° C., or heat treated for apredetermined time (e.g., about 0.5 to 2 hours) after suchthermosetting; or a thin white reflective film with a thickness of, forexample, preferably 100 μm or less and further preferably 50 μm or lessthat allows easy volatilization of the low-molecular-weight siloxanetherein is preferably formed and then heat treated, by using a hot-aircirculating oven. The content of the low-molecular-weight siloxane inthe white reflective film can be quantified by using gas chromatography.In the case of soft silicone such as silicone rubber, since largeamounts of low-molecular-weight siloxane tend to be generated, it isnecessary to conduct treatment for lessening the low-molecular-weightsiloxane by, for example, heating under vacuum or by curing and thenheating for long hours at a high temperature. In the case of acrosslinkable silicone resin, the amount of low-molecular-weightsiloxane generated is less, even without conducting such treatment.Particularly, since crosslinkable silicone resin particles includelow-molecular-weight cyclic siloxane in very small amounts, generationof low-molecular-weight siloxane can be suppressed for the amount of thecrosslinkable silicone resin particles that are used.

In order to form a white reflective film wherein the content oflow-molecular-weight 4-mer to 20-mer siloxanes is 100 ppm or less, it ispreferable to use the ink wherein the content of low-molecular-weight4-mer to 20-mer siloxane is preferably 300 ppm or less and furtherpreferably 200 μm or less.

When thermosetting or heat treatment is conducted at 180 to 250° C., thelow-molecular-weight siloxane in the white reflective film can beremoved considerably. When the white reflective film is thin, with athickness of preferably 100 μm or less and further preferably 50 μm orless, the low-molecular-weight siloxane becomes more easily removable byheat treatment.

The content of the low-molecular-weight siloxane in the white reflectivefilm can be quantified by using gas chromatography. In terms ofpracticality, the white reflective film using soft silicone such assilicone rubber contains a relatively large amount of thelow-molecular-weight siloxane, and therefore needs to undergo treatmentfor lessening the low-molecular-weight siloxane by heating under vacuumor by curing and then heat treating for long hours (e.g., 4 hours ormore) at a high temperature. In the white reflective film of the presentembodiment that includes a cured product of the crosslinkable siliconeresin, the content of the low-molecular-weight siloxane is small, evenwithout conducting such treatment.

Particularly, when thermosetting is conducted at a temperature of 180°C. or more, the low-molecular-weight 4 mer to 20-mer siloxanesufficiently vaporizes; and a white reflective film wherein theproportion of such siloxane is, for example, preferably 100 ppm or less,further preferably 50 ppm or less, and particularly preferably 10 ppm orless can be obtained. The low-molecular-weight 4-mer to 20-mer siloxanemay also be further lessened by conducting heat treatment in adecompression oven.

It is preferable that the content of the low-molecular-weight siloxaneis small, not only in the hard white reflective film described above,but also in the white reflective film using conventional silicone resinor silicone rubber.

For application in an electronic circuit assembly and the like whichrequire such white reflective film wherein the proportion of thelow-molecular-weight 4-mer to 20-mer siloxane is small, the whitereflective film may not necessarily need to have a pencil scratchhardness of 8 B or higher. For example, when a flexible substrate usinga polyimide sheet is used, if the white reflective film is hard, thefilm would crack or peel off as its curvature is increased or as its usebecomes more frequent; and therefore, the white reflective film having,for example, a low degree of pencil scratch hardness of lower than 8 Bmay be used for increased adhesion. When light emission associated withheat generation from an LED element needs to be considered for the whitereflective film, or when the white reflective ink is to be applied to asubstrate on the periphery of a high-powered LED or a solar photovoltaicelement, the pencil scratch hardness may be lower than 8 B in order toallow stabilization by reducing stress produced by thermal expansion. Insuch case, the coating is preferably heated and cured to vaporize andlessen the low-molecular-weight 4-mer to 20-mer siloxane.

(White Reflective Film)

The white reflective film formed as above has an initial reflectance forlight having a wavelength in a wide range of 420 to 900 nm including 550nm, that is preferably 80% or more, further preferably 85% or more,particularly 90% or more and especially 91% or more, and most preferably95% or more. The initial reflectance corresponds to the reflectance ofthe white reflective film immediately after curing; and absorbance at awavelength in a wide range can be measured by using a spectrophotometer,e.g., UV-3150 available from Shimadzu Corporation. Even after heattreatment is conducted at 150° C. for 100 hours, the reflectance ismaintained at preferably 80% or more, further preferably 85% or more,particularly preferably 90% or more and especially 91% or more, and mostpreferably 95% or more.

The pencil scratch hardness of the white reflective film is 8 B orhigher, preferably 6 B to 10 H, further preferably 2 B to 8 H, andparticularly preferably H to 7 H. The white reflective film with suchhardness has high scratch resistance and low tackiness. Therefore, sincescratches are not easily created on the surface and dust or the likedoes not easily attach to the surface, lowering in reflectance over timeis suppressed and the initial reflectance is maintained.

When the pencil scratch hardness is too high, although scratchresistance is excellent, cracks tend to occur. In order to suppressoccurrences of cracks, the pencil scratch hardness is preferably 7 H orlower. Specifically, when a rigid substrate that linearly expands suchas an aluminum substrate or a glass-reinforced epoxy substrate is usedas the base member, if the pencil hardness exceeds 7 H, microcrackswould tend to occur. In the case of a base member formed of a materialwith a very small linear expansion coefficient, such as a ceramicsubstrate, even if the pencil scratch hardness exceeds 7 H, microcrackswould not tend to occur. For the coating on a flexible base member suchas a film, the pencil scratch hardness is preferably B to 8 B to preventinhibition of flexibility.

The thickness of the white reflective film is preferably 10 to 500 μm,further preferably 20 to 300 μm, and particularly preferably 30 to 100μm. When the film is too thick, cracks tend to occur after curing. Whenthe film is provided on a flexible sheet or film, the film is made thinand to have a thickness of 5 to 70 μm and preferably 10 to 50 μm, to beable to conform to the flexibility. When the film is too thin, thetitanium oxide needs to be contained in high concentrations, in order toobtain an initial reflectance of 80% or more for light having awavelength in a wide range such as 420 nm to 900 nm which is a visiblespectrum. In such case, the coating becomes fragile and cracks tend tooccur therein.

The proportion of the titanium oxide particles in the white reflectivefilm is preferably adjusted arbitrarily in accordance with the thicknessof the white reflective film. In order to obtain an initial reflectanceof 80% or more for light having a wavelength in a wide range such as 420to 900 nm, the titanium oxide particles are preferably included in highconcentrations when the film is thin; and when the film is thick, highreflectance is obtained even with the titanium oxide particles includedin low concentrations. According to studies conducted by the presentinventors, results were obtained as shown in Table 1 below, with respectto the relation among: the thickness of the white reflective film; theamount of the titanium oxide particles included relative to 100 parts bymass (solid content) of the crosslinkable silicone resin; and thereflectance of light at 550 nm.

TABLE 1 Reflectance at Included parts 550 nm Thickness (μm) (parts bymass) (%) 10 50 64 100 82 150 88 250 93 20 50 73 100 88 150 91 250 95 3050 81 100 92 150 94 200 96 300 96 50 50 88 100 95 150 96 100 50 93 10097 150 98

According to the results in Table 1, for example, in order to obtain areflectance of 90%, 250 parts by mass are preferably included when thethickness is 10 μm; about 150 parts by mass are preferably included whenthe thickness is 20 μm; about 100 parts by mass are preferably includedwhen the thickness is 30 μm; an amount of about slightly more than 50parts by mass is preferably included when the thickness is 50 μm; andabout 50 parts by mass is preferably included when the thickness is 100μm.

Regarding the tackiness of the surface of the white reflective film, forexample, vapor-deposited aluminum powder with an average particle sizeof 25 μm is evenly sprayed on the entire surface of the white reflectivefilm; an excess of the evaporated aluminum powder that has overlappinglyaccumulated or that has lightly attached is blown away by using, from adistance of 100 mm, an air gun with a nozzle diameter of 2 mm and an airemission of 160 L/min; and then, the film surface is swept with anon-woven fabric; and with respect to reflectance for light having awavelength of 550 nm, the percent decrease between that before sprayingand that after sweeping with a non-woven fabric is preferably 5% orless, further preferably 3% or less, and particularly preferably 1% orless. In the case of such low tackiness, due to excellentnon-stickiness, there would be suppression of lowering in reflectancewith time that is caused by attachment of dust during use.

The white reflective film of the present embodiment preferably maintainsa high adhesion. Specifically, for example, in the case of conducting across-cut test in compliance with JIS K5400 wherein: a cross-cut patternof vertical and horizontal cuts spaced 1 mm apart is created on thewhite reflective film by using a cutter blade, thereby to prepare a testpiece; CELLOTAPE™ available from NICHIBAN Co., Ltd. is attached to thetest piece; and then the tape is swiftly pulled and separated, among the100 squares of the cross-cut pattern that are formed, the number of thesquares without separation of the coating is preferably 60 or more,further preferably 80 or more, particularly preferably 90 or more, andfurther particularly preferably 95 or more, and it is most preferable ifall of the squares are without separation of the coating. Thecombination of hardness and adhesion can be adjusted by the kind of Rgroup and the combination of D units, T units, and Q units and theirproportions in the silicone resin; the composition of the siliconeresin; the adjustment of cross-linkage degree of the silicone resin byusing silicone rubber, crosslinkable silicone oil, or the like; thecontent of the titanium oxide particles; and a coupling agent, aprimer/adhesive component, or the like.

[Embodiment 2]

A description will be given of steps in a method for forming a whitereflective film by screen printing, with reference to FIGS. 1A-1F. InFIGS. 1A-1F, Reference Nos. 1 and 11 denote an ink which is a siliconevarnish containing titanium oxide particles, and Reference No. 3 denotesa base member. Reference No. 4 denotes a screen mesh used in screenprinting. The screen mesh 4 comprises: a mesh portion 4 a; an aperture 4b; and a frame 4 c. Reference Nos. 5 and 6 denote a scraper and asqueegee, respectively. Reference Nos. 10 and 30 denote a coating.Reference Nos. 20 and 40 denote a white reflective film.

Formation of a white reflective film by screen printing is conducted inthe following steps. First, as in FIG. 1A, a screen mesh 4 is arrangedabove a base member 3. Then, an ink 11 is placed on the screen mesh 4.Next, as in FIG. 1B, with use of a scraper 5, the ink 11 is spread inthe direction of the arrow and thus forced into an aperture 4 b. Then,as in FIG. 1C, a squeegee 6 is moved in the direction of the arrow whilebeing pressed against the screen mesh 4 and the base member 3. Then, asin FIG. 1D, the ink 11 is transferred onto the base member 3. Then, thetransferred ink 11 is left for a predetermined time for leveling, sothat the gaps between the ink masses corresponding to the mesh patternof the screen mesh are filled. As such, as in FIG. 1E, a coating 30 ofthe ink 11 is formed on the base member 3. Then, as in FIG. 1F, thecoating 30 is cured to form a white reflective film 40.

When the present inventors attempted to form a white reflective film bya screen printing process using ink containing titanium oxide particlesin high concentrations, they faced a problem of having difficulty inobtaining a white reflective film with a high degree of pencil hardness.As a result of extensive studies to solve this problem, they found outthe following. That is, when the surface of the while reflective filmformed by a screen printing process was magnified and observed, thesurface was found to have an uneven mesh-like texture pattern(hereafter, also referred to as mesh marks) clearly remaining thereon.FIG. 6 shows an example of an image of the surface of the whitereflective film obtained by a screen coating process, magnified about147 times.

For example, when only a crosslinkable silicone liquid resin notincluding titanium oxide particles were screen printed, leveling of theink after separation of the screen mesh resulted in a smooth coatingsurface without any mesh marks. From the above, the cause of formationof mesh marks was studied; and this lead to the following observation.That is, a crosslinkable silicone liquid resin typically has a lowsolution viscosity (e.g., less than 10 Pa·sec). Therefore, the presentinventors found out that when only such crosslinkable silicone liquidresin with a low solution viscosity was screen printed as a resincomponent, as in FIG. 2, during leveling of the ink after separation ofthe screen mesh 4, only the crosslinkable silicone liquid resin 9flowed; whereas titanium oxide particles 8 with a high specific gravitythat were nearly aggregated as if forming a stone wall, tended not toseparate easily, and remained in that state. The present inventorspresumed that this resulted in formation of the mesh marks describedabove. Moreover, they presumed that during leveling of the ink, only thecrosslinkable silicone liquid resin 9 were thermally cured while thetitanium oxide particles 8 remained motionless in a state of nearaggregation, thereby causing mesh marks to remain. Still moreover, in apencil hardness test, since the pencil got caught on such uneven meshmarks remaining on the white reflective film, the present inventorsfound out that the uneven mesh marks caused the white reflective film toseparate and the degree of pencil hardness to lower. Based on suchfindings, the present inventors studied extensively on how to break downthe aggregates of the titanium oxide particles that were the cause offorming uneven mesh marks.

In Embodiment 2, a description will be given of a method for forming awhite reflective film with a high degree of pencil hardness bysuppressing occurrences of uneven mesh marks being the cause of loweringthe degree of pencil hardness, in the case where a white reflective filmis formed by a screen printing process by using, as ink, a siliconevarnish containing titanium oxide particles in high concentrations.

In the method for forming a white reflective film by a screen printingprocess of Embodiment 2, ink that is used contains a crosslinkablesilicone liquid resin, crosslinkable silicone resin particles, andtitanium oxide particles, the ink containing 10 to 500 parts by mass ofthe titanium oxide particles relative to a solid content of a total of100 parts by mass in the crosslinkable silicone liquid resin and thecrosslinkable silicone resin particles. By using such ink, duringleveling or thermosetting of the coating, the titanium oxide particlesthat are unevenly distributed in regions with formation of mesh marksare made to flow. As a result, a white reflective film having a smoothsurface whereon formation of mesh marks is suppressed, is obtained.

The method for forming a white reflective film of Embodiment 2 will bedescribed with reference to FIGS. 1A-1F.

In the method of forming a white reflective film of Embodiment 2, first,an ink 1 is prepared. The ink 1 contains a crosslinkable silicone liquidresin, crosslinkable silicone resin particles, and titanium oxideparticles, the ink containing 10 to 500 parts by mass of the titaniumoxide particles relative to a solid content of a total of 100 parts bymass in the crosslinkable silicone liquid resin and the crosslinkablesilicone resin particles.

Preferably 0.5 to 50 mass %, further preferably 1 to 30 mass %, andparticularly preferably 3 to 15 mass % of the crosslinkable siliconeresin particles are contained in the total solid content in thecrosslinkable silicone liquid resin and the crosslinkable silicone resinparticles. When the proportion of the crosslinkable silicone resinparticles is too large, the solution viscosity of the ink becomes toohigh, and printability and applicability of the ink tend to lower. Incontrast, when the proportion of the crosslinkable silicone resinparticles is too small, the effect of including the crosslinkablesilicone resin particles cannot be sufficiently obtained with ease, andleveling ability of the ink tends to lower. The average particle size ofthe crosslinkable silicone resin particles or the composite particles isnot particularly limited and is preferably about 0.5 to 100 μm, furtherpreferably about 10 to 80 μm, and particularly preferably about 15 to 50μm. When the average particle size of the crosslinkable silicone resinparticles or the composite particles is too large, for example, duringscreen printing, the particles tend not to pass through the screen mesheasily and thus remain in the residual ink from squeegeeing; andtherefore, the amount of the particles in the coating tends to decrease.When the average particle size of the crosslinkable silicone resinparticles or the composite particles is too small, melt flowabilitylowers at the time of thermosetting, and the effect of improvingleveling ability of the ink tends to be insufficiently obtained.

The proportion of the titanium oxide particles in the ink is 10 to 500parts by mass, preferably 20 to 400 parts by mass and further preferably30 to 300 parts by mass relative to the solid content of 100 parts bymass in the crosslinkable silicone liquid resin and the crosslinkablesilicone resin particles. When the proportion of the titanium oxideparticles exceeds 500 parts by mass, the white reflective film becomesfragile. In contrast, when the proportion of the titanium oxideparticles is less than 10 parts by mass, sufficient reflectance cannotbe obtained unless the coating is made thick. However, when the coatingis made too thick, the white reflective film becomes fragile. To theink, as in Embodiment 1, substances other than the titanium oxideparticles such as an inorganic white filler, an organic or inorganicfluorescent substance, an additive, and the like may be added.

Regarding the cured film of silicone obtained when the crosslinkablesilicone resin is cured, when the cured film is formed to have athickness of 50 μm, the pencil scratch hardness is 9 B or higher,preferably 3 B to 7 H, and further preferably F to 6 H. Such cured filmpreferably contains siloxane units of D units and siloxane units of Tunits, and is a dimethyl straight resin wherein the R group is a methylgroup or a methyl phenyl-based straight resin wherein the R group is acombination of a methyl group and a phenyl group; and particularly, thedegree of functionality (number of moles of T units/number of moles of Dunits) derived from the ratio between the D units and the T units ispreferably 2.6 to 2.9 and further preferably 2.6 to 2.8; and theproportion of the phenyl group in the R group is preferably 20 to 60 mol% and further preferably 30 to 50%. As necessary, the crosslink densitycan be adjusted by including a crosslinkable silicone oil or amonofunctional reactive dilutent. The degree of hardness can also belowered by mixing in a resin component with a low degree of hardnesssuch as silicone rubber.

Considering that low-molecular-weight cyclic siloxane causes insulationfailure on an electronic circuit, by using the crosslinkable siliconeresin particles, low-molecular-weight cyclic siloxane can be lessenedconsiderably; and this allows suppression of adverse effects to anelectronic material caused by the low-molecular-weight cyclic siloxanethat vaporizes from the white reflective film, such as non-conduction ona circuit. More specifically, in a silicone rubber ink obtained bypolymerization with low-molecular-weight cyclic siloxane as the startingmaterial, 20000 to 10000 ppm (2 to 1%) of the low-molecular-weightcyclic siloxane remains as an unreacted substance. Therefore, there is ahigh possibility of the low-molecular-weight cyclic siloxane vaporizingdue to heat during shaping, thereby causing pollution inside the oven;or of the resultant film becoming an insulating film on an electroniccircuit on a substrate; and there is a possibility of about 200 ppm ofthe low-molecular-weight cyclic siloxane remaining on the shapedproduct. In contrast, in the case of the crosslinkable silicone resinparticles, since the material is reactive low-molecular-weight siloxane,most of the material polymerizes during curing, thereby forming a hardfilm; and with hardly any unreacted substance, the remaininglow-molecular-weight cyclic siloxane is 10 ppm or less.

By using the ink containing such crosslinkable silicone liquid resin,crosslinkable silicone resin particles, and titanium oxide particles,the ink containing 10 to 500 parts by mass of the titanium oxideparticles relative to a solid content of a total of 100 parts by mass inthe crosslinkable silicone liquid resin and the crosslinkable siliconeresin particles, a coating is formed on a base member by screenprinting. Specifically, first, as in FIG. 1A, a moderate amount of theink 1 is mounted on top of a screen mesh 4.

The form of the screen mesh is not particularly limited if capable offorming a coating with an intended thickness. A specific example is ascreen mesh having a wire width of preferably about 20 to 70 μm andfurther preferably about 25 to 60 μm, a mesh size of preferably about 30to 250 μm and further preferably about 60 to 180 μm, and a screenthickness of 30 to 200 μm and preferably 40 to 100 μm.

Subsequently, as in FIG. 1B, with use of a scraper 5, the ink 1 isspread in the direction of the arrow and thus forced into an aperture 4b. Then, all of the apertures 4 b are filled with the ink 1. Then, as inFIG. 1C, a squeegee 6 is moved in the direction of the arrow while beingpressed against the screen mesh 4 and the base member 3, thereby totransfer the ink 1 to the base member 3 as in FIG. 1D.

Subsequently, as in FIG. 1E, the applied ink 1 is left for apredetermined time, thereby to spread and level the ink 1. As such, acoating 10 comprising the ink 1 is formed on top of the base member 3.

The coating thickness of the coating formed by leveling is notparticularly limited and is preferably 10 to 500 μm, further preferably20 to 300 μm, and particularly preferably 30 to 200 μm at the time ofcuring. When the coating is too thick, the white reflective film formedtends to become fragile. When the coating is too thin, the titaniumoxide needs to be contained in higher concentrations in order to obtaina sufficiently high reflectance; and in such case also, the whitereflective film tends to become fragile.

Subsequently, as in FIG. 1F, the coating 10 is thermally cured, therebyto form a white reflective film 20 on top of the base member 3. Theconditions for thermosetting is similar to those for Embodiment 1.During the early stage of the thermosetting process, the viscosity ofthe crosslinkable silicone liquid resin lowers. At that time, thecrosslinkable silicone resin particles maintain a relatively high meltviscosity, and therefore presumably moves while also breaking down theaggregates of the titanium oxide particles. Due to the meltedcrosslinkable silicone resin particles moving while also breaking downthe aggregates of the titanium oxide particles, there is achieved aleveling whereby a highly smooth surface is formed.

[Embodiment 3]

In Embodiments 1 and 2, descriptions were given of methods for forming awhite reflective film by using ink. According to such methods forforming a white reflective film by using ink, it may be difficult toapply the ink to a base member having portions that arethree-dimensional or portions where there is a mix of regions withdifferent heights, such that the resultant coating would have a uniformthickness. Specifically, when ink is used, formation of the coating mayresult in a smooth surface because outline of any subtle depressions andprojections on the surface of base member would be covered. In suchcase, the shapes of regions with different heights may not be reflectedon the surface of the white reflective film. The present inventors foundthat, by using a powder coating material for forming a white reflectivefilm, even when the base member had a surface shape with differentheights, the powder coating material was able to be applied in uniformthickness without the surface shape being covered. In the following,Embodiment 3 based on such finding will be given in detail.

A powder coating material is particularly effective in application tothe inner surface of a housing for a lighting device, whereon an evencoating is unlikely to be formed when a varnish-like ink is used; to theinner surface of cases of various devices; and onto a substrate with athree-dimensional form such as a three-dimensional substrate or a moldedbody.

In Embodiment 3, a description will be given of a method of forming awhite reflective film by using a powder coating material for whitereflective film containing: a crosslinkable silicone solid resin; and 10to 500 parts by mass of titanium oxide particles relative to 100 partsby mass of the crosslinkable silicone solid resin. Specifically, forexample, crosslinkable silicone resin flakes or powder and titaniumoxide particles are kneaded together, and the resultant kneaded productis made into powder form to prepare composite particles. Then, a powdercoating material containing such composite particles is sprayed and thusapplied to a base member that is made electrostatic, followed by curing,thereby to form a white reflective film.

In the following, a detailed description will be given of the method offorming a white reflective film by using the powder coating material forwhite reflective film, according to Embodiment 3.

The powder coating material for white reflective film in Embodiment 3contains the crosslinkable silicone solid resin, and contains 10 to 500parts by mass of the titanium oxide particles relative to 100 parts bymass of the crosslinkable silicone resin. The powder coating materialfor white reflective film preferably comprises the composite particlesincluding the crosslinkable silicone solid resin and the titanium oxideparticles, because when in such form, handling is easy and quality afterapplication is stable. The powder coating material may also be a mixtureof such composite particles and crosslinkable silicone resin particlesnot including titanium oxide or may also be a mixture of such compositeparticles and titanium oxide particles. The powder coating material mayalso be powder of a mixture of the titanium oxide particles andcrosslinkable silicone resin particles not including titanium oxideparticles. The powder coating material may also include three kinds ofparticles, i.e., the composite particles, crosslinkable silicone resinparticles not including titanium oxide, and titanium oxide particles.

As necessary, powder-coatable resin components other than thecrosslinkable silicone resin may be included inside the compositeparticles and/or inside the crosslinkable silicone resin particles inthe powder coating material, or may be included as an independentcomponent. Such resin components not particularly limited if formed of aresin conventionally used as a binder in a powder coating material.Specific examples include a fluorocarbon resin, an acrylic-based resin,a polyester-based resin, an epoxy-based resin, and a phenolic-basedresin, in particle form. In terms of excellent adhesion, an epoxy-basedresin is particularly preferred; and in terms of excellent lustrousness,a polyester-based resin is particularly preferred. In terms of excellentchemical stability of factors such as heat resistance and discolorationresistance, a fluorocarbon resin is preferred.

The proportion of the crosslinkable silicone resin in the total amountof all of the resin components is 50 mass % or more, and is preferably60 mass % or more, further preferably 80 mass % or more, andparticularly preferably 90 mass % or more. When the proportion of thesilicone resin in the total amount of all of the resin components isless than 50 mass %, light reflectance lowers with time. Particularly,when the powder coating material includes 50 mass % or more of a resinhaving an unsaturated bond such as a polyester-based resin or anepoxy-based resin, the resultant white reflective film tends undergoyellow discoloration with time.

The proportion of the titanium oxide particles in the powder coatingmaterial for white reflective film is 10 to 500 parts by mass,preferably 20 to 400 parts by mass, and further preferably 30 to 300parts by mass. When the proportion of the titanium oxide particles isless than 10 parts by mass, it becomes difficult to obtain an initialreflectance of 80% or more for light having a wavelength in a wide rangesuch as 420 to 900 nm. When the proportion of the titanium oxideparticles exceeds 500 parts by mass, electrostatic coating becomesdifficult; and also, coating formability degrades such that, forexample, the coating becomes fragile and cracks occur therein.

To the powder coating material for white reflective film in the presentembodiment, as in Embodiments 1 and 2, substances other than thetitanium oxide particles such as an inorganic white filler, an organicor inorganic fluorescent substance, an organic or inorganic pigment, andan additive may be added.

A production method of the powder coating material for white reflectivefilm in the present embodiment will be described. In production of thepowder coating material for white reflective film, first, acrosslinkable silicone solid resin in flake or powder form, other resincomponent(s) to be included as necessary, titanium oxide, and othermaterials are arranged to have a composition as given above, and thenpreliminarily mixed using a Henschel mixer, a ball mill, or the like.Then, the material mixture obtained from preliminary mixing is meltedand kneaded while being heated, using an extruder or heated rolls.Melting and kneading are preferably conducted at a temperature equal toor more than the melting point of the crosslinkable silicone solidresin, and less than the curing temperature. For example, when themelting point of the crosslinkable silicone solid resin is 110° C. andthe curing temperature is 180° C., melting and kneading are conducted at110° C. or more and less than 180° C.

The melted mixture obtained is finely pulverized using a pulverizer suchas a jet mill or an atomizer. Then, coarse particles and fine particlesare removed using a cyclone classifier or the like, to adjust particlesize. As such, a powder coating material for white reflective film isobtained. As necessary, concentration may be minorly adjusted orphysical property of the film may be adjusted, by adding crosslinkablesilicone resin particles having a separately-adjusted particle size andnot including titanium oxide, titanium oxide particles, or both. Thepowder coating material need not be such composite particles, and may bea mixture obtained by mixing the crosslinkable silicone resin particlesand the titanium oxide particles, without conducting any kneading.

The composite particles of the powder coating material for whitereflective film and the particles of the crosslinkable silicone resinare not particularly limited in particle size; and their averageparticles sizes are preferably about 0.5 to 100 μm, further preferablyabout 10 to 80 μm, and particularly preferably about 15 to 50 μm.

After the powder coating material for white reflective film obtained isapplied to the surface of the base member, the powder layer is leveledby conducting heating and melting at a temperature equal to or more thanthe melting point of the crosslinkable silicone resin particles, e.g.,70° C. to 130° C. Thereafter, the resultant undergoes a baking treatmentat 150° C. to 250° C. and is thus cured, thereby to form a whitereflective film.

For the application method, any conventionally-known powder applicationmethod can be used without particular limitation. Specific examplesinclude fluidized dip coating, thermal spraying, electrostatic fluidizeddip coating, and electrostatic powder spraying. Before applying thepowder on the base member, it is preferable to conduct, as necessary, achemical surface treatment or a physical surface treatment such ascorona discharge treatment, plasma treatment, ultraviolet lighttreatment, flame treatment, ITRO treatment, surface rougheningtreatment, priming treatment whereby a silane coupling agent is applied,blasting treatment, chemical etching, rubbing treatment, or cleaningtreatment using an organic-based solvent; or a combination of a chemicalsurface treatment and a physical surface treatment.

Regarding the condition for baking treatment conducted after leveling ofthe applied powder layer by heating and melting, heat treatment ispreferably conducted for about 60 to 20 minutes at a temperature usedfor heating and curing resin which is, for example, 100° C. to 350° C.,preferably 130° C. to 300° C., and further preferably 150° C. to 250° C.The temperature for heating and curing is selected in view of factors ofthe base member such as glass transition temperature, melting point,thermal expansion coefficient, relative difference in thermal expansioncoefficient between the base layer and the white reflective film, andheat resistance.

[Application]

The white reflective film according to each Embodiment is preferablyused as a reflector to be formed on a light source mount such as acircuit board for mounting a light source such as LED, to be formed onthe surface of a submount for mounting a light-emitting element such asan LED element, or to be incorporated into a solar cell assembly inorder to reflect entering light for concentration into a photovoltaicelement; or, as a reflector for more effectively conducting light from alight source to a light-conducting plate or sheet. Such white reflectivefilm is not only used for electrical and electronic purposes, but canalso be preferably used as a reflector for advertising displays,signboards, as well as products likely to be exposed to external heat orsunlight.

Specifically, for example, the white reflective film is used as areflector with high reflectance, for example: by being formed as a whitereflective film 50 on a circuit board 13 whereon a light source 60 suchas an LED is mounted, such that circuits 61 surrounding the light source60 are protected, as in FIG. 3; or by being formed on the surface of asubmount for an LED element. Moreover, for example, as in FIG. 4, awhite reflective film 71 formed on a lighting shade 70 serves as areflector for reflecting light emitted from a light source 72 mounted ona mount substrate 74 provided with a heat-radiating plate 73, to a sidewhere the light is to be applied.

EXAMPLES

Next, the present invention will be more specifically described by wayof Examples. The following Examples, however, are not to be construed aslimiting in any way the scope of the present invention.

First, evaluation methods used in the present Examples will be describedon the whole, as follows.

(Pencil Scratch Hardness Test)

Evaluation for pencil scratch hardness was conducted in compliance withJIS K5600-5-4, using the white reflective film formed on the aluminumplate. That is, pencils having various degrees of hardness and sharpenedto a predetermined state were each inclined at an angle of 45° andpointed onto the film surface, and then moved while being applied with apredetermined load. The hardness of the pencil with the greatest degreeof hardness that did not create any scratch marks was regarded as thepencil scratch hardness. The above test was conducted five times, andevaluation was made based on their average.

(Measurement of Initial Reflectance and Reflectance after AcceleratedAging Treatment)

Reflectance of light having a wavelength of 220 to 1000 nm immediatelyafter curing of the white reflective film formed on the aluminum plate,was measured using a UV-3150 spectrophotometer (available from ShimadzuCorporation).

Subsequently, the white reflective film formed on the aluminum plateunderwent an accelerated aging treatment at 150° C. for 100 hours, andthereafter, the reflectance was measured again in a similar manner.Then, the percent decrease in reflectance for light having a wavelengthof 550 nm, between that before and that after the accelerated agingtreatment {(initial reflectance−reflectance after agingtreatment)/initial reflectance×100}, was calculated.

(Dust Attachment)

To evaluate dust attachment, vapor-deposited aluminum powder (NihonKoken Kogyo Co., Ltd./Alumiflake #40) with an average particle size of25 μm was evenly sprayed onto the entire surface of the white reflectivefilm formed on the aluminum plate; an excess of the vapor-depositedaluminum powder that had overlappingly accumulated or that had lightlyattached was blown away by using, from a distance of 100 mm, an air gunwith a nozzle diameter of 2 mm and an air emission of 160 L/min, andthen swept with a non-woven fabric; and then the percent decrease inreflectance by the remaining vapor-deposited aluminum powder for lighthaving a wavelength of 550 nm {(initial reflectance−reflectance afteraluminum powder attachment)/initial reflectance×100}, was calculated.

(Adhesion)

Following a cross-cut test in compliance with JIS K5400, a cross-cutpattern of vertical and horizontal cuts spaced 1 mm apart was formed onthe coating by using a cutter blade, thereby to prepare a test piece;CELLOTAPE™ available from NICHIBAN Co., Ltd. was attached to the testpiece; and then the tape was swiftly pulled and separated. Among the 100squares of the cross-cut pattern that were formed, the number of thesquares without separation of the coating was counted; and 80 or more,less than 80 and 60 or more, and less than 60 were evaluated as A, B,and C, respectively.

(Content of Low-Molecular-Weight Siloxanes of 4-Mer to 20-Mer and 4-Merto 10-Mer)

From about 1 g of the white reflective film taken as a sample,low-molecular-weight siloxanes were extracted in carbon tetrachloride.Then, by using gas chromatography, the amounts of thelow-molecular-weight 4-mer to 10-mer and 4-mer to 10-mer siloxanes inthe extract liquid were quantified. Gas chromatography was conductedunder the conditions of using helium gas as carrier gas, using astainless steel column of 3 m filled with silica, and increasing thetemperature to 300° C. at a rate of temperature increase of 10° C./min.

(Presence and Non-Presence of Mesh Marks)

The surface of the white reflective film obtained was magnified about147 times, and smoothness of the surface was visually evaluated on thefollowing basis.

-   A: No mesh marks can be observed.-   B: Mesh marks can be observed in small amounts or partially.-   C: Mesh marks can be clearly observed on the entire surface.

Example 1

An ink for forming a white reflective film was prepared as follows.Relative to a solid content of 100 parts by mass in a dimethyl-basedstraight silicone resin varnish (dimethyl-based straight silicone resinvarnish “KR-242A” available from Shin-Etsu Chemical Co., Ltd.; pencilscratch hardness when cured film (hereafter referred to as cured resinfilm) is formed to have a thickness of 50 μm: 5 H) with a solutionviscosity of 0.012 Pa·sec, 200 parts by mass of rutile-type titaniumoxide (SR-1 available from Sakai Chemical Industry Co., Ltd.; averageparticle size: 0.25 μm; surface treated with Al₂O₃) were added. Then,the arranged composition was kneaded by using a 3-roller mill touniformly disperse the rutile-type titanium oxide, thereby to prepare aliquid ink with a solution viscosity of 10 Pa·sec.

The obtained ink was applied to an aluminum plate, a copper plate, aceramic plate, and a glass-reinforced epoxy plate (glass-epoxysubstrate) such that the thicknesses of coatings after curing became 50μm. This was followed by heat treatment at 180° C. for 20 minutes tocure the coatings, thereby to obtain white reflective films. Then,evaluation was conducted based on the above-described evaluationmethods. The results are shown in Table 2.

TABLE 2 Example No. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex.8 Ex. 9 Ex. 10 Ex. 1 Resin Dimethyl- Acryl- Polyester- Epoxy- MethylMethyl Methyl Methyl Dimethyl- Dimethyl- Silicone based modifiedmodified modified phenyl- phenyl- phenyl- phenyl- based based rubberstraight resin resin resin based based based based straight straightsilicone straight straight straight straight silicone silicone resinsilicone silicone silicone silicone resin resin resin resin resinresin + Reactive diluent Titanium oxide 200 200 200 200 200 200 200 200200 200 200 (parts by mass) Film thickness (μm) 50 50 50 50 50 50 50 5050 200 50 Pencil scratch hardness 5H 4H 3H H F 2B 4B 8B 5H 6H — of whitereflective film Reflectance 420 nm 89 86 87 81 87 89 80 84 87 95 87 (%)450 nm 99 96 97 89 97 100 86 93 90 101 95 550 nm 95 92 93 90 92 96 93 9192 97 94 750 nm 91 88 89 87 88 92 91 87 85 94 90 900 nm 86 83 84 82 8288 87 83 80 90 85 550 nm 94 92 93 84 92 91 88 90 91 96 94 after heattreatment (150° C. × 100 hrs) Percent 0.949 0.543 −0.108 7.301 0.1086.023 5.711 1.099 1.087 1.031 0.213 decrease after heat treatment (%)Dust 1 or 1 or 1 or 1 or 1 or 1 or 1 or 1 or 1 or 1 or 8 attachmentlower lower lower lower lower lower lower lower lower lower (%)Adherence Aluminum A A A A A A A A C A C plate Copper plate A B A B A AA A C A C Ceramic A B A B A A A A A A C plate Glass- A B A B A A A A C AC reinforced epoxy plate Amount of D4 to D10 1.7 2.3 1 5 1 2 2 10 1 5 5low- D4 to D20 3.2 14.8 4 783 13.5 51 15 50 6 10 150 molecular- weightD4 to D10 siloxane (ppm)

Example 2

An ink was prepared as in Example 1, except that an acryl-modifiedsilicone resin varnish (acryl-modified silicone resin varnish KR-9706available from Shin-Etsu Chemical Co., Ltd,; pencil scratch hardness ofcured resin film: 3 H) was used instead of the dimethyl-based straightsilicone resin varnish. Then, coatings were formed as in Example 1,except that the above ink was used instead of the ink used in Example 1;and the coatings were cured by heat treatment at 180° C. for 20 minutes.As such, white reflective films with a pencil scratch hardness of 4 Hwere formed and evaluated as in Example 1. The results are shown inTable 2.

Example 3

An ink was prepared as in Example 1, except that an polyester-modifiedsilicone resin varnish (polyester-modified silicone resin varnishKR-5235 available from Shin-Etsu Chemical Co., Ltd,; pencil scratchhardness of cured resin film: 3 H) was used instead of thedimethyl-based straight silicone resin varnish. Then, coatings wereformed as in Example 1, except that the above ink was used instead ofthe ink used in Example 1; and the coatings were cured by heat treatmentat 180° C. for 20 minutes. As such, white reflective films with a pencilscratch hardness of 3 H were formed and evaluated as in Example 1. Theresults are shown in Table 2.

Example 4

An ink was prepared as in Example 1, except that an epoxy-modifiedsilicone resin varnish (epoxy-modified silicone resin varnish ES-1023available from Shin-Etsu Chemical Co., Ltd,; pencil scratch hardness ofcured resin film: H) was used instead of the dimethyl-based straightsilicone resin varnish. Then, coatings were formed as in Example 1,except that the above ink was used instead of the ink used in Example 1;and the coatings were cured by heat treatment at 180° C. for 20 minutes.As such, white reflective films with a pencil scratch hardness of H wereformed and evaluated as in Example 1. The results are shown in Table 2.

Example 5

An ink was prepared as in Example 1, except that a methyl phenyl-basedstraight silicone resin varnish (methyl phenyl-based straight siliconeresin varnish KR-311 available from Shin-Etsu Chemical Co., Ltd,; pencilscratch hardness of cured resin film: F) was used instead of thedimethyl-based straight silicone resin varnish. Then, coatings wereformed as in Example 1, except that the above ink was used instead ofthe ink used in Example 1; and the coatings were cured by heat treatmentat 180° C. for 20 minutes. As such, white reflective films with a pencilscratch hardness of F were formed and evaluated as in Example 1. Theresults are shown in Table 2.

Example 6

An ink was prepared as in Example 1, except that a methyl phenyl-basedstraight silicone resin varnish (methyl phenyl-based straight siliconeresin varnish KR-282 available from Shin-Etsu Chemical Co., Ltd,; pencilscratch hardness of cured resin film: 2 B) was used instead of thedimethyl-based straight silicone resin varnish. Then, coatings wereformed as in Example 1, except that the above ink was used instead ofthe ink used in Example 1; and the coatings were cured by heat treatmentat 180° C. for 20 minutes. As such, white reflective films with a pencilscratch hardness of 2 B were formed and evaluated as in Example 1. Theresults are shown in Table 2.

Example 7

An ink was prepared as in Example 1, except that an unmodified methylphenyl-based straight silicone resin varnish (methyl phenyl-basedstraight silicone resin varnish KR-271 available from Shin-Etsu ChemicalCo., Ltd,; pencil scratch hardness of cured resin film: 4 B) was usedinstead of the dimethyl-based straight silicone resin varnish. Then,coatings were formed as in Example 1, except that the above ink was usedinstead of the ink used in Example 1; and the coatings were cured byheat treatment at 180° C. for 20 minutes. As such, films with a pencilscratch hardness of 4 B were formed and evaluated as in Example 1. Theresults are shown in Table 2.

Example 8

An ink was prepared as in Example 1, except that a methyl phenyl-basedstraight silicone resin varnish (methyl phenyl-based straight siliconeresin varnish KR-271 available from Shin-Etsu Chemical Co., Ltd,; pencilscratch hardness of cured resin film: 4 B) with a reactive diluent(ME91/available from Momentive Performance Materials Japan LLC.) addedthereto was used instead of the dimethyl-based straight silicone resinvarnish. Then, coatings were formed as in Example 1, except that theabove ink was used instead of the ink used in Example 1; and thecoatings were cured by heat treatment at 180° C. for 20 minutes. Assuch, white reflective films H with a pencil scratch hardness of 8 Bwere formed and evaluated as in Example 1. The results are shown inTable 2.

Example 9

An ink was prepared as in Example 1, except that a methyl phenyl-basedstraight silicone resin varnish (methyl phenyl-based straight siliconeresin varnish KR-400 available from Shin-Etsu Chemical Co., Ltd,; pencilscratch hardness of cured resin film: 8 H) was used instead of thedimethyl-based straight silicone resin varnish. Then, coatings wereformed as in Example 1, except that the above ink was used instead ofthe ink used in Example 1; and the coatings were cured by heat treatmentat 180° C. for 20 minutes. As such, white reflective films I with apencil scratch hardness of 8 H were formed and evaluated as inExample 1. The results are shown in Table 2. Regarding evaluation forpencil scratch hardness, since cracks occurred in the white reflectivefilm formed on the aluminum plate due to difference in thermalexpansion, the white reflective film formed on the ceramic plate wasused.

Example 10

White reflective films were formed as in Example 1, except that the filmthickness was changed to 200 μm, and were then evaluated. The resultsare shown in Table 2.

Comparative Example 1

An ink was prepared as in Example 1, except that a 60 Shore A siliconerubber (LR3303/60 available from Wacker Asahikasei Silicone Co., Ltd.,)was used instead of the dimethyl-based straight silicone resin varnish.Then, coatings were formed as in Example 1, except that the above inkwas used instead of the ink used in Example 1; and the coatings werecured by heat treatment at 150° C. for 20 minutes, thereby to form whitereflective films J. The white reflective films J had low degrees ofhardness, and therefore could not be measured for pencil scratchhardness; but had a Shore A hardness of 60°. These films were evaluatedas in Example 1. The results are shown in Table 2.

Example 11

An ink for white reflective film was prepared as follows. Adimethyl-based straight silicone resin varnish (dimethyl-based straightsilicone resin varnish KR-400 available from Shin-Etsu Chemical Co.,Ltd.; silicone resin concentration: 100 mass %) with a solutionviscosity of 0.0012 Pa·sec; and a granular dimethyl-based straightsilicone resin (particles with an average particle size of 15 μmprepared by pulverizing and classifying YR3370 in solid form and havinga melting point of 109° C., available from Momentive PerformanceMaterials Japan LLC.), were prepared.

Subsequently, relative to a solid content of 100 parts by mass in thedimethyl-based straight silicone resin varnish, 6 parts by mass of thegranular dimethyl-based straight silicone resin and 200 parts by mass ofrutile-type titanium oxide (SR-1 available from Sakai Chemical IndustryCo., Ltd.; average particle size: 0.25 μm; surface treated with Al₂O₃)were added. Then, the arranged composition was kneaded by using a 3-rollmill, thereby to prepare an ink with a solution viscosity of 60 Pa·sec.In the solid content of the crosslinkable silicone resin components, theproportion of the granular dimethyl-based straight silicone resin was5.7 mass %.

Subsequently, the obtained ink was used to form a coating on top of analuminum plate by using a stainless screen mesh with a screen thicknessof 90 μm, such that the thickness of the coating after curing became 50μm. Then, the coating on the aluminum foil was heated at 130° C.,leveled, and then thermally cured by heat treatment at 180° C. for 60minutes, thereby to form a white reflective film with a thickness of 30μm. Then, evaluation was conducted as above. The results are shown inTable 3. FIG. 5 shows an image of when the surface of the whitereflective film obtained in Example 11 was magnified about 147 timeswith a microscope for observation.

TABLE 3 Example No. Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17Proportion 5.7 2.0 0.5 9.0 16.6 5.7 0 of granular silicone (mass %) Meshmark A A B A A A C Pencil 6H 6H 5H 6H 7H 6H 5H scratch hardnessReflectance 97 95 95 96 97 97 95 (%, 550 nm)

Example 12

An ink was prepared as in Example 11, except that, relative to a solidcontent of 100 parts by mass in the dimethyl-based straight siliconeresin varnish, 2 parts by mass of the granular dimethyl-based straightsilicone resin were arranged instead of 6 parts by mass of the granulardimethyl-based straight silicone resin; and a white reflective film wasproduced and evaluated as in Example 11. In the solid content of thecrosslinkable silicone resin components, the proportion of the granulardimethyl-based straight silicone resin was 2.0 mass %. The results areshown in Table 3.

Example 13

An ink was prepared as in Example 11, except that, relative to a solidcontent of 100 parts by mass in the dimethyl-based straight siliconeresin varnish, 0.5 part by mass of the granular dimethyl-based straightsilicone resin was arranged instead of 6 parts by mass of the granulardimethyl-based straight silicone resin; and a white reflective film wasproduced and evaluated as in Example 11. In the solid content in thecrosslinkable silicone resin components, the proportion of the granulardimethyl-based straight silicone resin was 0.5 mass %. The results areshown in Table 3.

Example 14

An ink was prepared as in Example 11, except that, relative to a solidcontent of 100 parts by mass in the dimethyl-based straight siliconeresin varnish, 10 parts by mass of the granular dimethyl-based straightsilicone resin were arranged instead of 6 parts by mass of the granulardimethyl-based straight silicone resin; and a white reflective film wasproduced and evaluated as in Example 11. In the solid content of thecrosslinkable silicone resin components, the proportion of the granulardimethyl-based straight silicone resin was 9.0 mass %. The results areshown in Table 3.

Example 15

An ink was prepared as in Example 11, except that, relative to a solidcontent of 100 parts by mass in the dimethyl-based straight siliconeresin varnish, 20 parts by mass of the granular dimethyl-based straightsilicone resin were arranged instead of 6 parts by mass of the granulardimethyl-based straight silicone resin; and a white reflective film wasproduced and evaluated as in Example 11. Relative to the total solidcontent in the ink, the proportion of the rutile-type titanium oxide was62.5 mass % and the proportion of the crosslinkable silicone resincomponents (solid content) was 37.5 mass %. In the solid content in thecrosslinkable silicone resin components, the proportion of the granulardimethyl-based straight silicone resin was 16.6 mass %. The results areshown in Table 3.

Example 16

Composite particles comprising: a crosslinkable silicone resin; andtitanium oxide particles kneaded in the crosslinkable silicone resin,were prepared as follows. Relative to 100 parts by mass of adimethyl-based straight silicone resin as the crosslinkable siliconeresin, 200 parts by mass of rutile-type titanium oxide were arranged.Then, the arranged composition was uniformly mixed by using a Henschelmixer. Then, the mixture was melted and kneaded while being heated at80° C. by using a twin screw extruder, thereby to obtain a kneadedproduct. Then, the melted kneaded product was coarsely crushed at roomtemperature, followed by pulverization with a jet mill. The resultantwas sieved and composite particles with an average particle size of 35μm were prepared.

Instead of arranging the granular dimethyl-based straight siliconeresin, the composite particles prepared above were arranged; and an inkwas prepared such that the granular dimethyl-based straight siliconeresin was 6 parts by mass and the rutile-type titanium oxide was be 200parts by mass, relative to the solid content of 100 parts by mass in thedimethyl-based straight silicone resin varnish. Except that the aboveink was used, a white reflective film was produced and evaluated as inExample 11. The results are shown in Table 3.

Example 17

Except that 6 parts by mass of the granular dimethyl-based straightsilicone resin were not arranged relative to a solid content of 100parts by mass in the dimethyl-based straight silicone resin varnish, anink was prepared and a white reflective film was produced and evaluatedas in Example 11. The results are shown in Table 3. FIG. 6 shows animage of when the surface of the white reflective film obtained byscreen printing in Example 17 was magnified about 147 times with amicroscope for observation.

Example 18

A powder coating material for white reflective film for forming a whitereflective film was prepared as follows. Relative to 100 parts by massof a dimethyl-based straight silicone solid resin in powder form, 200parts by mass of rutile-type titanium oxide were arranged. For thedimethyl-based straight silicone solid resin, SILRES MK (pencil scratchhardness of 50 μm-thick cured film: HB, melting point: 50° C.) availablefrom Wacker Asahikasei Silicone Co., Ltd. was used. Then, the arrangedcomposition was uniformly mixed by using a Henschel mixer. Then, themixture was melted and kneaded while being heated at 80° C. by using atwin screw extruder, thereby to obtain a kneaded product. Then, themelted kneaded product was coarsely crushed at room temperature,pulverized with a jet mill, and then sieved. As such, a powder coatingmaterial for white reflective film with an average particle size of 35μm was prepared.

Subsequently, the obtained powder coating material for white reflectivefilm was applied to an aluminum plate by using a corona-typeelectrostatic powder coater, such that the thickness of coating aftercuring became 50 μm; then the coating was cured by heat treatment at180° C. for 30 minutes, thereby to obtain a white reflective film.

The results are shown in Table 4.

TABLE 4 Example No. Ex. 18 Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24Binder resin Silicone Silicone Silicone Silicone Silicone SiliconeSilicone resin 100% resin resin 100% resin resin 100% resin 100%resin/Silicone- 100% 100% modified polyester resin = 80%/20% Titaniumoxide (parts by mass) 200 200 200 200 200 100 200 Film thickness (μm) 5030 100 150 200 50 50 Reflectance 420 nm 90 84 90 90 91 88 89 (%) 450 nm98 96 99 99 100 97 97 550 nm 95 91 98 98 98 94 95 750 nm 91 85 94 95 9589 90 900 nm 85 79 89 90 91 83 86 550 nm, after 94 90 97 97 97 92 91heat treatment (150° C. × 100 hrs) 440 nm, after 97 95 98 98 98 95 93heat treatment (150° C. × 1000 hrs) Percent decrease 1.053 1.100 1.0201.020 1.020 2.128 4.211 after heat treatment (%) Pencil scratch hardnessof white 5H 4H 5H 6H 6H 5H 5H reflective film Adherence A A A A A A A

Examples 19 to 22

Except that the powder coating material were applied such that thethicknesses of the coatings after curing became 30 μm, 100 μm, 150 μm,and 200 μm, respectively, instead of 50 μm, white reflective films wereformed and evaluated as in Example 18.

Example 23

Except that application was conducted by using the powder coatingmaterial for white reflective film for which 100 parts by mass of therutile-type titanium oxide, instead of 20 parts by mass thereof, werearranged relative to 100 parts by mass of the dimethyl-based straightsilicone resin, a white reflective film was formed and evaluated as inExample 18.

Example 24

Except that application was conducted by using the powder coatingmaterial for white reflective film for which 80 mass % of thedimethyl-based straight silicone resin and 20 mass % of asilicone-modified polyester resin were arranged as a binder instead ofarranging only the dimethyl-based straight silicone resin as a binder, awhite reflective film was formed and evaluated as in Example 18.

The invention claimed is:
 1. A powder coating material for a whitereflective film comprising: a crosslinkable silicone solid resincomprising a crosslinkable straight silicone resin; and 10 to 500 partsby mass of titanium oxide particles relative to 100 parts by mass of thecrosslinkable silicone solid resin, wherein a proportion of thecrosslinkable silicone solid resin in a total amount of all resincomponents contained in the powder coating material is 50 mass % ormore.
 2. The powder coating material for a white reflective film inaccordance with claim 1 including 50 to 200 parts by mass of thetitanium oxide particles relative to 100 parts by mass of thecrosslinkable silicone solid resin.
 3. The powder coating material for awhite reflective film in accordance with claim 1, wherein thecrosslinkable silicone solid resin has a melting point of 45 to 200° C.4. A white reflective film having: an initial reflectance for lighthaving a wavelength of 550 nm of 80% or more; and a pencil scratchhardness of 4B or higher, the white reflective film comprising: a curedsilicone resin; and 20 to 500 parts by mass of titanium oxide particlesrelative to 100 parts by mass of the cured silicone resin, wherein: thewhite reflective film is formed on a surface of a base member, and thecontent of low-molecular-weight 4-mer to 20-mer siloxane is 100ppm orless.
 5. A white reflective film having: an initial reflectance forlight having a wavelength of 550 nm of 80% or more; and a pencil scratchhardness of 4B or higher, the white reflective film comprising: a curedsilicone resin; and 20 to 500 parts by mass of titanium oxide particlesrelative to 100 parts by mass of the cured silicone resin, wherein: thewhite reflective film is formed on a surface of a base member; aninitial reflectance for full-spectrum light over a wavelengths region of425nm to 780 nm is 90% or more; and after undergoing heat treatment at150° C. for 1000hours, a reflectance for light having a wavelength of440 nm is 90% or more.
 6. A light source mount having a white reflectivefilm formed on a light source mounting surface, the white reflectivefilm having: an initial reflectance for light having a wavelength of 550nm of 80% or more; and a pencil scratch hardness of 4B or higher, thewhite reflective film comprising: a cured silicone resin; and 20 to 500parts by mass of titanium oxide particles relative to 100 parts by massof the cured silicone resin.
 7. A lighting device shade having a whitereflective film formed on a surface on a light source side, the whitereflective film having: an initial reflectance for light having awavelength of 550 nm of 80% or more; and a pencil scratch hardness of 4Bor higher, the white reflective film comprising: a cured silicone resin;and 20 to 500 parts by mass of titanium oxide particles relative to 100parts by mass of the cured silicone resin.
 8. A white reflective filmhaving: an initial reflectance for light having a wavelength of 550 nmof 80% or more; and a pencil scratch hardness of 4B or higher, the whitereflective film comprising: a cured silicone resin of a crosslinkablesilicone resin including a crosslinkable straight silicone resin; and 20to 500 parts by mass of titanium oxide particles relative to 100 partsby mass of the cured silicone resin, wherein the white reflective filmis formed on a surface of a base member.
 9. The white reflective filmaccording to claim 8, wherein after undergoing heat treatment at 150° C.for 1000 hours, a reflectance for light having a wavelength of 440 nm is90% or more.